ATM based telecommunications networks are arranged with a number of ATM switch nodes communicating with one another. A design and structure of switch nodes are well known and may take a variety of different forms. As the switch nodes become increasingly large in terms of their capacity to handle data, the physical structure for the node may (and likely will) exceed one physical switch module of boards (for example, one rack). Thus, for many telecommunication nodes, the physical infrastructure for the node is often based on several physical switch modules, each containing a number of boards. The modules communicate with one another via internal links such that the entire system of modules acts as a single cohesive node unit. The reliability of the interconnection links between the several modules in such a large node is crucial. If any link fails between the number of modules, the entire operation of the node is jeopardized. Accordingly, physical redundancy in the interconnection links between modules within a node is preferable.
Several methods for link redundancy are present on the market that require the applications running at the node to closely participate in any changeover process from a first link to a redundant second one. Thus, as shown in FIG. 2, a switch node is viewed as a number of layers ranging from, in the example of FIG. 2, power distribution in the bottom layer 28 up to network layer routing and/or connection termination functions with application processing in the upper layer 20. The problem commonly associated with the prior art is that the upper layers (20) that run an application are involved in a changeover process from one interconnection link to another (at layer 22). Redundancy operations at layer 22 should occur independently, as much as possible, of the operations of the application in layer 20. If possible, redundancy changeovers at layer 22 should have no or very small interaction with other layers in FIG. 2.
The present invention isolates the interconnection link redundancy layer by re-routing of traffic flows, either packets or cells, from a failed first interconnection link to another redundant such link between interconnected switch modules, without any involvement of functions in the higher layer. When a connection is set up, a state condition is determined as to which one within a pair of switch module interconnection links is the primary link over which the packet flow on the connection shall be routed. A corresponding routing tag is then attached to each packet on the node-internal connection. If the state of the selected interconnection links changes to a non-operational state, the packet routing will be changed by means of changing the translation of the routing tag within the interconnection link layer so that the packets will be forwarded via the secondary link. Interconnection link redundancy is obtained with minimal interaction to the application layer.
With the present invention, interconnection link redundancy is obtained with minimal interaction to the application layer.
These, as well as other objects and advantages of this invention, will be more completely understood and appreciated by careful study of the following more detailed description of a presently preferred exemplary embodiment of the invention taken in conjunction with the accompanying drawings, of which: